This invention generally relates to processes and compositions for the extraction and/or recovery of precious metal contained in precious metal-bearing materials or ores. The invention also relates to treatment and purification of water. Generally, the term "precious metals" is intended to cover a wide range of valuable metals, including, but not limited to, silver, gold, platinum group elements, molybdenum, copper and zinc.
Conventional methods of precious ore extraction are already well known. Thus, the prior art teaches extraction of such metals from naturally occurring ore, either in situ or after the ore has been mined. Leaching with the use of chloride and hypochlorite ions is a well known method for extracting precious metals from ores.
With respect to gold, there are generally three main forms of this precious metal which occur in nature. In this document, "gold" is intended to include such metals as platinum, iridium, rhodium, ruthenium, palladium, silver, osmium and other metals. The first form of gold comprises free gold particles within the ore, while the second includes gold as part of a compound with other minerals in the ore. A third type of gold is sometimes referred to as "incorporated gold", where the atoms of gold are incorporated, for example, in a quartz lattice between atoms of silica and oxygen. Thus, microparticles of gold may be incorporated into a mineral such as quartz, and this form of gold cannot easily be recovered or released. The gold in this category may also be dispersed as a colloid, namely, a system of gold atoms in a crystal lattice. Isomorphic gold, comprising individual gold atoms in the points of lattice is yet a further form of incorporated gold. The last three forms of gold in the category of incorporated with other mineral particles are extremely difficult to extract.
The prior art shows numerous examples showing different methods for extraction of metals from ore. U.S. Pat. No. 3,910,636 (Hard) generally describes a process of in situ mining which requires the drilling of a well into an underground ore deposit, and thereafter introducing a leach solution to contact the ore. The leach solution dissolves the mineral within the ore deposit, and the pregnant solution is recovered and processed for the purpose of obtaining the particular mineral dissolved therein.
U.S. Pat. No. 4,342,592 (Lamb) generally describes the production of silver or gold by processing silver- or gold-bearing ore with solutions containing chloride and hypochlorite ions. Further, the chloride/hypochlorite solution may be regenerated electrochemically and reused, rather than being discharged. The process, which is stated to have a non-polluting effect, has three basic steps, namely, metal solubilization, metal recovery and solution regeneration.
U.S. Pat. No. 4,439,235 (Simpson) discloses a chlorination process which can, in a relatively short period of time and without using cyanide compounds, solubilize gold, silver and other precious metals contained within oxide, sulfide and carbonaceous ore. In this patent, the process involves comminuted ore contacted first with an acidic primary leach solution and then with a basic secondary leach solution. In the process, hydrochloric acid is used as a catalyst.
U.S. Pat. No. 4,557,759 (McGrew) teaches the use of an iodine leach for the dissolution of gold. Gold is recovered from gold ores by oxidation with iodine and complexation with iodide in an aqueous, electrically conductive leach or lexiviant. U.S. Pat. No. 4,734,171 also describes gold recovery by iodide/iodine leaching with the pregnant lexiviant containing solubilized gold and iodine being treated in an electrolytic cell to reduce gold in solution to elemental gold.
Several other patents also show the chlorination of metals including the use thereof for recovery of the metal. U.S. Pat. No. 4,567,812 (von Hahn) makes the chloride of the metal from the sulfide of that metal through a number of steps, and recovery of the metal chloride from an aggregate mixture produced by the process. U.S. Pat. No. 4,723,998 (O'Neil) teaches gold recovery from ores through extraction by a procedure involving a simultaneous chlorine leach and ion exchange resin adsorption procedure. U.S. Pat. No. 5,169,503 (Baughman) teaches the solubilization of metal values by a lexiviant comprising an aqueous solution of chloride salt and hypochlorite salt. U.S. Pat. No. 5,328,669 (Han) also attempts to extract metals from their ores while avoiding the use of cyanide or strong acids. The method of this patent teaches charging to a reaction zone the precious-metal-bearing materials, water, either a halide or an elemental halogen, and ammonium ions as a leaching solution. Separation and recovery steps for the precious metal-ion-solution follow.
U.S. Pat. No. 4,592,779 (Russ) attempts to recover a higher percentage by weight of precious metals from raw ores including treatment with an aqueous basic solution having a pH in the range of about 12 to about 14. The basic solution may contain an alkali metal or alkaline earth metal hydroxide, such as sodium hydroxide. After treatment with the aqueous basic solution, suspended precious metals are separated by conventional methods such as carbon absorption, electrowinning or precipitation.
U.S. Pat. No. 4,752,412 (van Antwerp) describes a slurry including the formation of "activated oxygen" comprising hydroxyl (OH), atomic oxygen, hydrogen peroxide, hydrogen dioxide (HO.sub.2) and hydrogen peroxide dimers and trimers, as well as ozone.